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EBSD characterization of bobbin friction stir welding of AA6082-T6 aluminium alloy

Tamadon A., Pons D. J., Clucas D.

Advances in Materials Science

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2020

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Vol. 20, nr 4(66)

49--74

EN

Electron Backscatter Diffraction (EBSD) was used to determine microstructural evolution in AA6082-T6 welds processed by the Bobbin Friction Stir Welding (BFSW). This revealed details of grain-boundaries in different regions of the weld microstructure. Different polycrystalline transformations were observed through the weld texture. The Stirring Zone (SZ) underwent severe grain fragmentation and a uniform Dynamic Recrystallisation (DRX). The transition region experienced stored strain which changed the grain size and morphology via sub-grain-boundary transformations. Other observations were of micro-cracks, the presence of oxidization, and the presence of strain hardening associated with precipitates. Flow-arms in welds are caused by DRX processes including shear, and low and high angle grain boundaries. Welding variables affect internal flow which affects microstructural integrity. The shear deformation induced by the pin causes a non-uniform thermal and strain gradient across the weld region, leading to formation of mixed state transformation of grain morphologies through the polycrystalline structure. The grain boundary mapping represents the differences in DRX mechanism I different regions of the weld, elucidates by the consequences of the thermomechanical nature of the weld. The EBSD micrographs indicated that the localised stored strain at the boundary regions of the weld (e.g. flow-arms) has a more distinct effect in emergence of thermomechanical nonuniformities within the DRX microstructure.

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Characterization of dissimilar Al-Cu BFSW welds; interfacial microstructure, flow mechanism and intermetallics formation

Tamadon A., Abdali M., Pons D. J., Clucas D.

Advances in Materials Science

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2020

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Vol. 20, nr 3(65)

52--78

EN

The purpose of this study is to elucidate the flow features of the dissimilar Al-Cu welded plates. The welding method used is Bobbin Friction Stir Welding (BFSW), and the joint is between two dissimilar materials, aluminium alloy (AA6082-T6) and pure copper. Weld samples were cut from along the weld line, and the cross-sections were polished and observed under an optical microscope (OM). Particular regions of interest were examined under a scanning electron microscope (SEM) and analysed with Energy Dispersive X-ray Spectroscopy (EDS) using the AZtec software from Oxford Instruments. The results and images attained were compared to other similar studies. The reason for fracture was mainly attributed to the welding parameters used; a higher rotational speed may be required to achieve a successful BFSW between these two materials. The impact of welding parameters on the Al-Cu flow bonding and evolution of the intermetallic compounds were identified by studying the interfacial microstructure at the location of the tool action. The work makes an original contribution to identifying the solid-phase hybrid bonding in Al-Cu joints to improve the understanding of the flow behaviours during the BFSW welding process. The microstructural evolution of the dissimilar weld has made it possible to develop a physical model proposed for the flow failure mechanism.

3

Optimization of process parameters on friction stir welding of AA 6082-T6 butt joints using Taguchi method

Arab M., Zemri M.

Mechanics and Mechanical Engineering

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2018

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Vol. 22, nr 4

1371--1380

EN

Friction Stir Welding (FSW) was carried out on Aluminum Alloy 6082-T6 plates with dimensions of 200 x 70 x 2 mm. Design of Experiment (DOE) was applied to determine the most important factors which influence the Ultimate Tensile Strength (UTS) and Hardness (HV) of AA 6082-T6 joints produced by Friction Stir Welding (FSW). Effect of two factors which include tool rotational speed and welding speed on (UTS, HV) were investigated by Taguchi method using L9 orthogonal array to find the optimum process parameters. An analysis of variance (ANOVA) was carried out to determine which of the selected factors are more significant on both of responses, the optimum parameters for the higher UTS it found by using a rotational speed of 1400 rpm and 125 mm/min for the welding speed, also 1400 rpm and 160 mm/min to maximize Hardness (HV).